This invention relates to the detection of hydrazine compounds and particularly to the detection of hydrazine, monomethylhydrazine (MMH) and unsymmetrical dimethylhydrazine (UDMH) in gaseous samples using a technique whereby these compounds are converted to hydrazine derivatives which may readily be analyzed, as by oxidation to produce detectable nitric oxide (NO) gas.
Hydrazine compounds are used in a number of specialized commercial and military applications. Small amounts of hydrazine, for example, are often added to boiler water to retard corrosion, and hydrazine is also used as a fuel in rockets. Monomethylhydrazine (MMH) is employed as a propellant in space vehicle thrusters, and unsymmetrical dimethylhydrazine (UDMH) forms a major component of fuels for certain missiles. Since leakage or spillage of even small amounts of hydrazine compounds can yield harmful pollutants or lead to risk of explosion, it is often desirable to monitor samples, particularly air samples, for these compounds.
Various devices are known for detecting hydrazine compounds. Among these are infrared or photoacoustic spectrometers, electrochemical sensors containing electrolyte or ceramic beads which react when contacted by hydrazines, and colorimetric sensors. For example, U.S. Pat. No. 4,309,262 discloses a detector for hydrazine compounds which uses a ceramic pellet containing iridium to decompose fumes of the compounds and generate detectable heat.
Known hydrazine detectors, particularly those intended for detection of hydrazine compounds in gas samples, typically have one or more disadvantages which limit their utility. One common deficiency is a lack of selectivity due to interferences with other airborne compounds such as ammonia, oxygen, carbon dioxide, vehicular exhaust gases, and other organic compounds. Another drawback is a high level of maintenance required because of the need to replenish electrolyte, paper tape, or scrubbers or to make frequent corrections for drift. Many devices lack the sensitivity to detect hydrazines at the detection levels desired, and some (e.g., mass spectroscopy) are quite expensive and/or so complex as to require a highly skilled operator.
Other drawbacks of known hydrazine compound detectors are their inability to accurately perform analyses due to condensation or sticking of hydrazine compounds in sampling lines leading to the detector or in the detector itself.
Accordingly, it is an object of the invention to provide an improved method and apparatus for detecting hydrazine compounds.
It is a particular object of the invention to provide an improved apparatus for detecting hydrazine, monomethylhydrazine (MMH), and unsymmetrical dimethylhydrazine (UDMH) in gaseous samples.
It is an object of the invention to provide a method and apparatus for quantitative, continuous measurement of hydrazine compounds in gaseous samples.
It is an object of the invention to provide an improved method and apparatus for detecting hydrazine compounds in gaseous samples which permits low-loss sample transport along long lines, as from local sampling locations to a central analyzer.
It is also an object of the invention to provide a hydrazine compound detector which has high sensitivity, selectivity, and stability.